Device and method for sensing and indicating inclination of an automotive vehicle

ABSTRACT

A device and method used to indicate vehicle inclination and conditions indicative of a potential rollover is disclosed. The device and method may be embodied in original equipment or in an aftermarket product in a manner so that the driver may easily determine the vehicle inclination. For example, the device and method may be embodied in a mirror assembly mounted in the vehicle. The device and method may also be used to detect the rate of change of inclination to provide a warning of adverse driving conditions. The device and method may also include a compass that indicates a corrected heading of the vehicle.

BACKGROUND OF THE INVENTION

1. Field

The present invention relates to automotive vehicle instrumentation and,more particularly, to instrumentation for sensing and indicatinginclination of the vehicle.

2. Related Art

Some automotive vehicles may have a propensity to rollover under certainadverse driving conditions, such as when in an aggressive turn or on asteep incline. This is primarily due to their high center of gravity.Automotive engineers have been challenged by consumer demands to producevehicles having a high center of gravity (such as sport utilityvehicles) while reducing or eliminating the propensity of these vehiclesto rollover.

At the same time, drivers of these vehicles tend to acclimate to thevehicle's behavior under various driving conditions, thereby decreasingthe potential for driver-induced rollovers. However, this may not alwaysbe the case. For example, in multi-vehicle households, wherein onevehicle is a sport utility vehicle and the other is either a sports caror a sedan, the driver may not be immediately conditioned to the degreeof responsiveness of each vehicle. In this respect, sports carstypically have exceptional handling around sharp curves, due to theirlow center of gravity; whereas, sport utility vehicles do not. As aresult, driving style enjoyed in the sports car may have adverse effectsif used in the sport utility vehicle.

Therefore, systems have been developed to provide information to thedriver about a vehicle's inclination. One example of such a system isdescribed in U.S. Pat. No. 5,825,284. This system includes multiplesensors mounted at multiple structural locations on the vehicle,resulting in a relatively complex detection and indication system.

SUMMARY OF THE INVENTION

The present invention is a simple device and a method used to provideinformation about vehicle inclination and conditions that would indicatethe potential of a rollover. The device and method may be embodied inoriginal equipment or in an aftermarket product that allows the driverto readily and easily determine the vehicle's inclination. The deviceand method may also be used to warn of a possible rollover condition.The device and method may also utilize the inclination information toindicate a corrected heading of the vehicle.

In one embodiment of the invention, a mirror assembly for use in avehicle is disclosed. The mirror assembly includes a frame, a mirrormounted to the frame and an indicator mounted to the frame. Theindicator communicates directly or indirectly with a sensor that isresponsive to at least one of pitch angle and roll angle of the vehicle.The indicator indicates the at least one of pitch angle and roll angle.

In another embodiment, a multiple use mirror assembly for use in a motorvehicle is disclosed. The mirror assembly includes a mirror frame havinga mirror fixed thereto and means for adjustably securing the mirrorframe to the motor vehicle. The mirror assembly also includes anindicator integrally secured to the mirror assembly and simultaneouslyvisible with reflections in the mirror. At least one sensor for sensingat least one of pitch angle and roll angle of the motor vehicleindependently of the relative position of the mirror frame and mirrorrelative to the vehicle is operatively connected to the indicator. Theindicator indicates the sensed at least one of pitch angle and rollangle of the vehicle.

In another embodiment, an apparatus for detecting inclination of avehicle is disclosed. The apparatus includes a controller and a sensorcommunicating with the controller. This sensor is responsive to at leastone of pitch angle and roll angle of the vehicle. The controllercalculates a rate of change of the at least one of pitch angle and rollangle based on the at least one of pitch angle and roll angle of thevehicle sensed by the sensor.

In yet another embodiment, a method of detecting inclination of avehicle is disclosed. The method includes sensing at least one of pitchangle and roll angle of the vehicle, and calculating a rate of change ofthe at least one of pitch angle and roll angle.

In still another embodiment, a method of detecting inclination of avehicle is disclosed. The method includes sensing at least one of pitchangle and roll angle of the vehicle, comparing the at least one ofsensed pitch angle and roll angle to at least one threshold, andcomparing the at least one of sensed pitch angle and roll angle to adifferent threshold based upon vehicle operating conditions.

In yet another embodiment, a method of reducing false alarms in a devicefor detecting inclination of a vehicle is disclosed. The method includessensing at least one of pitch angle and roll angle of the vehicle,calculating a rate of change of the at least one pitch angle and rollangle of the vehicle, and warning only if the rate of change of the atleast one of pitch angle and roll angle of the vehicle exceeds a firstthreshold value and does not exceed a second threshold value.

In another embodiment, a device in a vehicle is disclosed. The vehiclehas a vehicle plane defined by the plane through which the rotationalaxes of the wheels of the vehicle pass. The device includes a sensor forsensing lateral acceleration of the vehicle in the vehicle plane. Thedevice also includes a controller communicating with the sensor. Thecontroller calculates a rate of change of the lateral acceleration andcompares the calculated rate of change to a threshold. The devicefurther includes an indicator communicating directly or indirectly withthe controller. The indicator indicates a warning when the calculatedrate of change exceeds the threshold.

In another embodiment, a method of detecting inclination of a vehicle isdisclosed. The method includes sensing at least one of pitch angle androll angle of the vehicle to provide a static signal; calculating a rateof change of the at least one of pitch angle and roll angle to provide atransient parameter; combining the static signal and the transientsignal to provide a combined inclination parameter; and, comparing thecombined inclination parameter to a threshold.

In another embodiment, a mirror assembly for use in a vehicle isdisclosed. The mirror assembly includes a frame and a mirror mounted tothe frame. A compass is coupled to the frame. The compass detects aheading of the vehicle. The compass communicates with a controller thatcommunicates with a sensor that is responsive to at least one of pitchangle and roll angle of the vehicle. The controller corrects thedetected heading of the vehicle based on the sensed at least one ofpitch angle and roll angle of the vehicle. An indicator is mounted tothe frame. The indicator indicates the corrected heading.

Various embodiments of the present invention provide certain advantagesand overcome certain drawbacks of prior devices and systems. Embodimentsof the invention may not share the same advantages and those that do maynot share them under all circumstances.

Further features and advantages of the present invention as well as thestructure and method of making various embodiments of the presentinvention are described in detail below with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the invention will now be described, by way ofexample, with reference to the accompanying drawings, in which:

FIG. 1 is a prior art mirror assembly;

FIG. 2 is a mirror assembly according to one aspect of the presentinvention embodying a device for indicating vehicle inclination;

FIG. 3 is a diagrammatic representation of the device for indicatingvehicle inclination;

FIG. 4 is a diagrammatic representation of a mounting location of themirror assembly of FIG. 2;

FIG. 5 is a view taken along line 5—5 of FIG. 4;

FIG. 6 is a flow chart according to one aspect of the invention;

FIG. 7 is a flow chart of another aspect of the invention;

FIG. 8 is a flow chart of another aspect of the invention; and

FIG. 9 is a flow chart of another aspect of the invention.

DETAILED DESCRIPTION

According to one aspect of the invention, a device provides the driverwith information about the inclination of the vehicle in an easilydiscernable manner. The inclination information is preferably displayedin the driver's normal field of view. In addition, the device may besupplied as original equipment in the vehicle or as an aftermarket item.To accommodate either of these goals, in one embodiment, an indicatorfor the device is embodied in a mirror assembly, such as a rearviewmirror assembly.

Prior mirror assemblies include various indications of desiredparameters. As shown in FIG. 1, a prior art mirror assembly 20 includesa frame 22 and a mirror 24 mounted to the frame. The mirror assembly 20further includes an indicator 26 for indicating the interior or exteriortemperature 28 and the heading 30 of the vehicle.

In the embodiment described with reference to FIG. 2, a mirror assembly32 includes a frame 34 and a mirror 36 mounted to the frame 34, as inthe prior art mirror assembly. The mirror assembly 32 also includes anindicator 38 mounted to the frame 34. However, rather than displayinginterior or exterior temperature and the heading of the vehicle, as inthe prior art mirror assembly, additionally or alternatively, theindicator indicates the pitch angle 40 of the vehicle or the roll angle42 of the vehicle or both the pitch and roll angles.

Although FIG. 2 shows the indicator as a visual display device, such asan LED display, the present invention is not limited in this respect asother suitable indicators may be employed. For example, the indicatormay be an audible indicator that emits tones depending on the parameterto be indicated. Further, the indicator may be a horizon indicator thatdisplays both pitch and roll.

In another illustrative embodiment, the mirror assembly 32 may alsoinclude a compass to indicate the heading and/or a thermometer toindicate the temperature together with the pitch angle 40 and/or theroll angle 42 of the vehicle. When such a mirror assembly 32 displaysall such parameters, the default display may be the compass andthermometer. However, in one embodiment, the indicator 38 may beswitched from indicating the temperature and/or heading to indicatingthe pitch angle and roll angle of the vehicle. The driver can manuallychange the display with the use of a switch(es) or the display may bechanged automatically. Automatic switching may occur when a pitch angleor roll angle parameter exceeds a threshold, as will be more fullydescribed below. It should be appreciated that the present invention isnot limited in this respect and the all information (namely, heading,temperature, pitch angle and roll angle) may be simultaneouslydisplayed.

To detect the inclination of the vehicle, a suitable sensor(s) that isresponsive to the pitch angle or roll angle of the vehicle may beemployed. As shown in FIG. 3, a device 44 used to determine vehicleinclination, which may be embodied in the mirror assembly 32, includesthe indicator 38, one or more switches 46 and one or more sensors 48communicating directly or indirectly with the indicator 38. The one ormore sensors 48 may communicate with each other and with the controlleror with the controller independently of communicating with each other.The device 44 may also include a controller 50 and may also communicatewith a power supply 52, as will be further described below. In thisembodiment, sensor(s) 48 are incorporated into the mirror assembly 32.However, the present invention is not limited in this respect and othersuitable locations for the sensor(s) may be employed. For example, thesensor(s) and/or controller may be mounted at a location apart from theindicator 38 and/or the mirror assembly 32.

The mirror assembly 32 of FIG. 2 may be mountedin any vehicle, such as asport utility vehicle, multi-passenger vehicle, sports car, sedan, ortruck, to name a few, at any suitable location. When the mirror assemblyis embodied as a rearview mirror (as opposed to a sideview mirror), themirror assembly 32 is mounted at an overhead location in a passengercompartment 54 of a vehicle 56, as shown in FIGS. 4 and 5. In somevehicles, the mirror assembly 32 may be mounted to the windshield 57 orto the roof 58.

As is known, the rearview mirror is mounted to the windshield or roof sothat the mirror may be positioned in a desired orientation. This may beaccomplished using any suitable mechanism, such as a ball and socketjoint. As described above, in one embodiment, the sensor(s) 48 ismounted in the mirror assembly 32. In this embodiment, the sensor(s) 48is mounted to the fixed portion of the mirror assembly (i.e., fixedrelative to the vehicle). Thus, as shown in FIG. 4, the mirror assembly32 includes a mount 59 fixed relative to the vehicle 56, to positionablymount the frame 34. A pod 61, which is fixedly mounted to the mount 59,houses the sensor(s) 48.

Mounting the sensor(s) in a fixed position (i.e., stationary relative tothe vehicle) reduces the necessity to recalibrate the device each timethe mirror is repositioned. However, the present invention is notlimited in this respect. Therefore, when the sensor(s) is mounted in themovable part of the mirror assembly, one or more switches may be used torecalibrate the device.

Although, in one embodiment, the indicator 38 is incorporated into themirror assembly, the invention is not limited in this respect. Thus, theindicator 38 may be located in any suitable location, such as in anoverhead console, in the vehicle dashboard or within the instrumentdisplay panel, to name a few. Further, the device itself may beincorporated into a stand-alone unit or it may be supplied in discretecomponents, each suitably mounted in the vehicle.

Continuing with reference to FIG. 3, the device 44 includes or otherwisecommunicates with the controller 50. The controller 50 may be part ofthe vehicle's controller or a stand-alone processor, as desired. Thecontroller 50 includes a CPU (not shown), RAM (not shown) and a computerstorage medium such as ROM (not shown). The ROM, which may be anelectronically programmable chip, typically includes a computer readablecode encoded therein. The controller may also include an input/outputbus (not shown). The computer program allows the controller to performthe various desired functions. The device may also include a stand-alonepower supply such as a battery, the vehicle power system, or solar powersupply, as desired.

In one embodiment, the controller 50 communicates with the sensor(s) 48,manipulates the signal from the sensor(s) and signals the indicator todisplay desired information or otherwise alert the driver of changingconditions. Switch(es) 46 also communicates with the controller 50 tocontrol the device in any desired manner.

In one embodiment, the controller 50 is a stand-alone processor mountedin the mirror assembly. For example, the controller 50 is mounted in thepod 61 (see FIGS. 4 and 5). The power supply 52 to the controller 50,sensor(s) 48 and indicator 38 is from the vehicle's power supply.Further the indicator 38 is an LED display. The sensor(s) 48 includesensor(s) to sense the pitch angle of the vehicle, the roll angle of thevehicle, the heading of the vehicle and/or the exterior and/or interiortemperature.

As described above, the sensor(s) 48 used to sense the pitch angle andthe roll angle of the vehicle may be any suitable sensor(s). One suchsensor is a digital accelerometer. A first accelerometer may be used tosense the roll angle of the vehicle; whereas, a second accelerometer maybe used to sense the pitch angle of the vehicle. Alternatively, in oneembodiment, a combined sensor capable of detecting both pitch angle androll angle may be employed. Such a sensor is available from AnalogDevices of Norwood, Mass., U.S.A. under the product name ADXL202 orADXL210 Dual Axis iMEMS Accelerometer with digital and/or analog output.Of course, those skilled in the art will recognize suitable alternativeor additional sensors or accelerometers may be employed.

As shown in FIGS. 4 and 5, the vehicle 56 includes a longitudinal axis63 that extends in the X direction and a lateral axis 65 that extends inthe Y direction and that is perpendicular to the longitudinal axis. Theaccelerometers (or accelerometer if the abovementioned or similar dualaxis accelerometer is used) are oriented in a manner to senseaccelerations in the X direction (longitudinal acceleration) and in theY direction (lateral acceleration). The accelerometers may be mounted inan orientation that is most sensitive to changes in inclination.Therefore, in one embodiment, the accelerometers may be oriented suchthat their sensitive axes are perpendicular to the force of gravity,such as in a plane that extends substantially parallel to the vehicleplane. The vehicle plane may be defined by the plane of the vehicle thatis parallel to the horizontal road surface. For example, the vehicleplane may be defined by the plane that passes through the rotationalaxes of the wheels (not shown) of the vehicle.

When the pitch angle sensor (i.e., the X-axis accelerometer or theX-axis value of the dual axis accelerometer) is oriented so that its Xaxis is parallel to the vehicle plane as described above, and once theoutput signal from the accelerometer has been converted to anacceleration that varies between −1 g and +1 g, the output may becalculated using the following equation:

Pitch angle=a sin(A _(x)/1 g),  [1]

where A_(x) is the acceleration sensed in the X direction of thevehicle.

When the roll angle sensor (i.e., the Y-axis accelerometer or the Y-axisvalue of the dual axis accelerometer) is oriented so that its Y axis isparallel to the vehicle plane as described above, and once the outputsignal from the accelerometer has been converted to an acceleration thatvaries between −1 g and +1 g, the output may be calculated using thefollowing equation:

Roll angle=a sin(A _(y)/1 g),  [2]

where A_(y) is the acceleration sensed in the Y direction of thevehicle.

In one embodiment, the X axis of the accelerometer used to senselongitudinal acceleration is aligned with the longitudinal axis of thevehicle and the Y axis of the accelerometer used to sense lateralacceleration is aligned with the lateral axis of the vehicle, with the Xaxis and the Y axis being orthogonal to each other. However, thoseskilled in the art will realize that these axes may be oriented in anydesired orientation (i.e. direction and/or relative angular orientation)provided that the output signals of the accelerometers are appropriatelycorrected to the longitudinal and lateral axes of the vehicle andparallel to the vehicle plane.

Further, those skilled in the art will recognize that up to about 30°,the pitch angle may be assumed to be the output of the acceleration inthe X direction, and the roll angle may be assumed to be the output ofthe acceleration in the Y direction. This is because sin α for smallangles is approximately equal to α in radians.

With the pitch and roll angle known, the controller 50 may indicatevarious information to the driver. As shown in FIG. 6, at box 60, thepitch and/or roll angle is sensed. At box 62, the controller 50 maysignal to the indicator 38 to display the pitch and/or roll angle of thevehicle. In one embodiment, it may be desirable to indicate a warningwhen the pitch and/or roll angle of the vehicle 56 exceeds a certainthreshold. Thus, as shown at box 64, the sensed pitch and/or roll angleis compared to a respective one or more thresholds. At box 66, if thesensed pitch and/or roll angle is below the one or more thresholds, thecontroller 50 continues to monitor the pitch and/or roll angle byreturning to box 60. If the sensed pitch and/or roll angle is above theone or more thresholds, a warning is indicated, as shown at box 68,which may be in the form of a visual or audible warning.

According to another aspect of the invention, the device 44 may be usedto detect whether driver behavior, if continued, could cause a potentialrollover condition. For example, if a driver were turning the vehicletoo quickly or cornering at a high rate of speed, it may be desirable towarn the driver so that corrective action may be timely taken.

Thus, in one embodiment, the controller 50 calculates a rate of changeof the sensed pitch and/or roll angle. With reference to FIG. 7, at box70, the pitch and/or roll angle of the vehicle 56 at time T1 is sensedand stored in memory. At box 72, the pitch and/or roll angle of thevehicle 56 at time T2 is sensed, and may be stored in memory. Next, atbox 76, the controller 50 calculates a rate of change of the pitchand/or roll angle and may display such information, as in box 74, asdesired. The calculated rate of change may be displayed, as indicated atbox 78. To determine whether or not the driving behavior represents apotential rollover condition, at box 80, the controller 50 compares thecalculated rate of change to a first threshold. If, at box 82, thecalculated rate of change is below the first threshold, the controller50 continues to respond to sensed pitch and roll angle by returning tobox 70. If the calculated rate of change of the pitch and/or roll angleis above the first threshold, the controller 50, at box 84, signals theindicator 38 to issue an appropriate warning. Although in oneembodiment, the controller calculates a rate of change based on sensedvalues, the present invention is not limited in this respect as suitablesensors that sense rate of change may be employed.

If the indicator is incorporated into the mirror assembly 32 describedabove and defaults to displaying heading and/or temperature, then, inone embodiment, the indicator 38 automatically switches from such adefault to indicating the pitch angle and roll angle data (whether it beabsolute values or rate of change values) when the rate of changeexceeds the first threshold.

Rather than utilizing the pitch angle and roll angle data individually,in some instances it may be desirable to use the sensed pitch angle androll angle of the vehicle 56 as a combined value. For example, assumethe vehicle is traversing a surface that is inclined downward and to theleft, such that the driver is forced to turn the vehicle. In such acircumstance and for a given speed, the vehicle 56 may have a propensityto rollover, even though any one of the pitch or roll angles wouldindividually not indicate a potential rollover condition.

Such a feature is described with reference to FIG. 8. At box 90, thesensor(s) 48 senses the pitch angle and, if desired, displays the pitchangle at box 92. At box 94, the sensor(s) 48 senses the roll angle and,if desired, displays the roll angle at box 96. At box 98, the controller50 calculates a combined pitch and roll angle. The combined pitch androll angle may also be displayed as desired, at box 100. The controller50 then compares the combined pitch and roll angle to a threshold, atbox 102. At box 104, the controller 50 determines whether the combinedpitch and roll angle is below a threshold. If it is, the controller 50continues to receive the pitch and roll angle data from the sensor(s).If the combined pitch and roll angle is greater than the threshold,then, at box 106, a warning is indicated. Also, in one embodiment, therate of change of the pitch angle and may be combined with the rate ofchange of the roll angle. This combined rate of change, like thecombined pitch and roll angle, may be compared to yet another threshold.In a further embodiment, a combined value that represents the combinedrate of change and the combined pitch and roll angle, may be compared tostill another threshold.

In this embodiment, the threshold is set to a value that may bedifferent than the value of any of the pitch or roll angle thresholdsindividually. Thus, as described above, if the combined pitch and rollangle exceeds such a threshold, a warning will be indicated. This isdesirable because, the driving conditions may require an alarm totrigger at a point that is different, for example, earlier, than whatwould otherwise occur based on the individually sensed pitch angle androll angle.

In any of the embodiments described above, the device may compensate forthe speed of the vehicle. Thus, the threshold to which the pitch angle,the roll angle, the rate of change thereof or the combined pitch androll angle is compared may be different, depending upon the speed of thevehicle. The controller 50 may receive data regarding the speed of thevehicle 56 using any desired method, including but not limited to,receiving data directly from the vehicle instrument panel viaappropriate signal wires, using global positioning systems, integratingthe sensed acceleration or using appropriate radar devices. It is to beappreciated, however, that the present invention is not limited in thisrespect as other methods may be used to receive speed data.

In some instances, road surface conditions are not always ideal and,thus, may have bumps or potholes. In such situations, a false alarm or afalse warning of potentially adverse conditions may occur. Therefore, inone embodiment, the device 44 may compensate for such irregularities inthe road surface. For example, a warning is triggered only when the rateof change of one of the pitch or roll angles is less than a thresholdvalue. In this respect, should the vehicle encounter a pothole, it islikely that the vehicle will pitch momentarily such that the rate ofchange of the pitch angle would be very large. To reduce the potentialfor a false alarm, a warning is indicated only when the rate of changeof the pitch or roll angle is below a certain threshold indicative ofthe large pitch angle but above a threshold which would indicate apotential rollover condition.

An example of this is shown with reference to FIG. 7. At box 122, thesensed rate of change is compared to a second threshold. If, at box 124,the rate is above the second threshold, then it is likely that thevehicle encountered a pothole, bump or other surface irregularity and noalarm would be indicated. If, at box 124, the rate is below the secondthreshold, but above the first threshold, then a warning is indicated asat box 84. Although the device may include a method to reduce falsealarms, the present invention is not limited in this respect. Therefore,as shown in FIG. 7, the feature to reduce false alarms is shown indashed lines.

According to another aspect of the invention, an alarm may be indicatedwhen the static inclination of the vehicle (i.e., pitch, roll, orcombined pitch and roll) combined with the rate of change of inclinationexceeds a threshold. The propensity of a vehicle to roll over may dependon the combination of vehicle inclination (i.e., static roll angle andpitch angle or combined pitch and roll angle) and transientaccelerations (i.e., rate of change of inclination). For example, if avehicle is already rolled to a particular angle, such as when traversinga hill side, an additional transient acceleration resulting from a rapidmaneuver or hitting a pot hole or bump either add or subtract from theroll over tendency. That is, if the vehicle is statically inclined in aparticular direction, then a given rate of change of inclination in thatdirection will more likely cause a roll over condition than if thevehicle had been inclined in the opposite direction.

Thus, as shown in FIG. 9, at box 120, the pitch and/or roll angle of thevehicle is sensed to produce a static angle parameter. At box 122, therate of change of the pitch angle and/or roll angle is calculated. Atbox 124, the static angle parameter and a parameter representing therate of change of the pitch angle and/or roll angle is combined toproduce a combined parameter. At box 126, the combined parameter iscompared to a threshold. If, at box 128, the combined parameter is belowthe threshold, the static angle continues to be monitored at box 120.If, at box 128, the combined parameter is above the threshold, then, atbox 130, a warning is indicated.

In one embodiment, this process may be carried out by the controllerusing the following equation:

Combined Parameter=K 1*Ω+K 2*dΩ/dT  [3]

where:

Ω is a vector representing the long term average of the roll angle;

dΩ/dT is a vector representing the rate of change of vehicle roll angle;and

K1 and K2 are weighting factors dependant upon vehicle parameters.

It should be appreciated that although the above described equation isuseful for the roll angle data, a similar equation may be employed forthe pitch angle data, if desired.

Any of the thresholds described above may be a function of variousvehicle parameters, such as, but not limited to, the moment of inertiaof the vehicle and the center of gravity of the vehicle. Thethreshold(s) may alternatively be set using empirical data. Thesethreshold(s) may be preloaded into the memory of the controller. In oneembodiment, it may be desirable to calibrate the device according tospecific vehicle parameters. This may be accomplished by activatingvarious switches to enter a calibration mode for the specific vehicle onwhich the device is to be installed. The thresholds may also be alearned parameter.

In addition, according to another aspect, the data from the Y-axisaccelerometer may be used to sense the lateral acceleration experiencedby the vehicle, for example, when in a turn. Thus, in one embodiment, itmay be desirable to set the threshold at a value that represents thedriver's reaction threshold. For example, assume the vehicle is in aturn on a highway exit ramp. If the driver suddenly jerked the wheel sothat the rate of change of the lateral acceleration exceeded a certainvalue, then a warning would alert the driver so that the driver couldtake corrective action.

According to another aspect of the invention, errors typically inherentin digital compasses may be corrected with the use of the one or moresensors 48, namely the accelerometers. Conventional automotive digitalcompasses are limited in their accuracy capabilities because of the lackof gimbaling. Since a magnetic compass is an instrument that can resolvethe direction of the horizontal component of the total Earth's magneticfield vector, every compass either provides a horizontal reference ormakes the assumption that the vehicle is level. In automotiveapplications, electronic compasses using magnetoresistive (MR) sensorsor fluxgate sensors typically have not been gimbaled because of theextra costs associated with gimbals. Rather, they work on the assumptionthat the vehicle is essentially level. In New England, for example, thevertical to horizontal ratio (Hz/Hx) of the Earth's magnetic field istypically four to one, decreasing to zero at the equator and approaching10 to 1 at high latitudes, such as in Alaska, for example. If a vehiclewere to ascend a 20° hill in an easterly or westerly direction, thecompass will show an±80° error. This phenomenon is often referred to as“gimbaling error” or “northerly turning error”, because the compass willdeflect to the north or south even though it is on an easterly orwesterly heading. Correcting for gimbaling error in vehicles capable ofdriving off-road is particularly advantageous, because in such vehicles,the vehicle is rarely level and the driver may be dependent on thecompass to determine a correct path for the vehicle.

The equation for gimbaling error when the vehicle is pitched on an angleis:

Error=Sin φ*Sin θ*Hz/Hx  [4]

Where:

θ is the pitch angle of the vehicle;

φ is the heading of the vehicle;

Hz is the vertical component of the Earth's magnetic field; and

Hx is the horizontal component of Earth's magnetic field.

A similar formula applies for a vehicle rolled on an angle when thevehicle is in a northerly or southerly heading.

Error=Cos φ*Sin β*Hz/Hx  [5]

Where:

β is the roll angle of the vehicle;

φ is the heading of the vehicle;

Hz is the vertical component of the Earth's magnetic field; and

Hx is the horizontal component of Earth's magnetic field.

Equations [4] and [5] can be combined as follows:

Total Error=Sin φ*Sin θ*Hz/Hx+Cos φ*Sin β*Hz/Hx  [6]

By utilizing the pitch angle and roll angle outputs of theaccelerometers filtered with a long time constant (and, in oneembodiment, adding a Z axis to the magnetometer array), it is possibleto remove these errors using the following equations:

H′x=Hx−K 1* Sin θ*Hz  [7]

H′y=Hy−K 2* Sin β*Hz  [8]

Where:

Hx is the measured earth's magnetic field vector along the X axis(vehicle longitudinal axis);

Hy is the measured earth's magnetic field vector along the Y axis(vehicle lateral axis); and

Hz is the measured earth's magnetic field vector along the Z axis(vehicle up-down axis).

The corrected heading is given by:

Heading=a tan(H′y/H′x)  [9]

Where H′y and H′x are the corrected X and Y vectors

Those skilled in the art will recognize that if the magnetic latitude ofa vehicle's location is known, an estimate of the vertical field can bemade, reducing the need for a Z axis field sensor with reduction in costand potentially some loss of accuracy.

Each of the elements described herein, or two or more together, may bemodified or may also find utility in other applications different fromthose described above. In addition, although the specific embodimentsdisclosed in the figures and described in detail employ particularcombinations, the present invention is not limited in this respect asvarious aspects of the invention can be employed together, separately orin different combinations. Thus, the particular embodiments described indetail are provided for illustrative purposes only. Those skilled in theart will recognize that various modifications and substitutions may bemade without departing in any way from the spirit of the presentinvention as defined by the following claims.

What is claimed is:
 1. A mirror assembly for use in a vehicle, themirror assembly comprising: a frame; a mirror mounted to the frame; andan indicator mounted to the frame, the indicator communicating directlyor indirectly with a sensor that is responsive to at least one of pitchangle and roll angle of the vehicle, the indicator indicating the atleast one of pitch angle and roll angle.
 2. The assembly according toclaim 1, wherein the indicator indicates a warning when the at least oneof pitch angle and roll angle exceeds a threshold.
 3. The assemblyaccording to claim 1, wherein the indicator indicates a warning when arate of change of the at least one of pitch angle and roll angle exceedsa threshold.
 4. The assembly according to claim 2, wherein the warningis at least one of an audible and a visual warning.
 5. The assemblyaccording to claim 3, wherein the warning is at least one of an audibleand a visual warning.
 6. The assembly according to claim 1, wherein theindicator communicates with at least one of a compass to indicate aheading of the vehicle and a thermometer to indicate temperature.
 7. Theassembly according to claim 6, wherein the indicator automaticallyswitches from indicating the at least one of the heading of the vehicleand the temperature to indicating the at least one of pitch angle androll angle of the vehicle when the at least one of pitch angle and rollangle exceeds a threshold.
 8. The assembly according to claim 6, whereinthe indicator automatically switches from indicating the at least one ofthe heading of the vehicle and the temperature to indicating the atleast one of pitch angle and roll angle of the vehicle when a rate ofchange of the at least one of pitch angle and roll angle exceeds athreshold.
 9. The assembly according to claim 6, further comprising amanually operated switch that operates to switch the indicator betweenindicating the at least one of the heading of the vehicle and thetemperature and indicating the at least one of pitch angle and rollangle of the vehicle.
 10. The assembly according to claim 1, incombination with the sensor, wherein the mirror assembly furthercomprises a mount to mount the frame to the vehicle, the sensor beingmounted to the mount.
 11. The combination according to claim 10, whereinthe mount, when attached to the vehicle, is stationary relative to thevehicle.
 12. The assembly according to claim 1, in combination with thesensor, wherein the sensor, when the mirror assembly is mounted to thevehicle, is stationary relative to the vehicle.
 13. The assemblyaccording to claim 1, in combination with the sensor and the vehicle,the sensor being mounted within the vehicle and apart from the mirrorassembly.
 14. The assembly according to claim 1, in combination with thevehicle.
 15. The combination according to claim 14, wherein the vehicleis a sport-utility vehicle.
 16. The assembly according to claim 1, incombination with the sensor, wherein the sensor comprises anaccelerometer.
 17. The combination according to claim 16, wherein theaccelerometer comprises a dual-axis accelerometer.
 18. The combinationaccording to claim 17, in combination with the vehicle, wherein theaccelerometer is mounted in a plane extending substantially parallel toa vehicle plane, the vehicle plane defined by a plane through whichrotational axes of wheels of the vehicle pass.
 19. An apparatus fordetecting inclination of a vehicle, the apparatus comprising: acontroller; a sensor communicating with the controller, the sensor beingresponsive to at least one of pitch angle and roll angle of the vehicle,the controller calculating a rate of change of the at least one of pitchangle and roll angle based on the at least one of pitch angle and rollangle of the vehicle sensed by the sensor; and an indicatorcommunicating with the controller, the indicator indicating the rate ofchange of the at least one of pitch angle and roll angle.
 20. Theapparatus according to claim 19, wherein the indicator indicates the atleast one of pitch angle and roll angle.
 21. The apparatus according toclaim 19, wherein the indicator indicates a warning when a rate ofchange of the at least one of pitch angle and roll angle exceeds athreshold.
 22. The apparatus according to claim 21, wherein the warningis at least one of an audible and a visual warning.
 23. The apparatusaccording to claim 19, wherein the sensor comprises an accelerometer.24. The apparatus according to claim 23, wherein the accelerometercomprises a dual-axis accelerometer.
 25. The apparatus according toclaim 24, in combination with the vehicle, wherein the accelerometer ismounted in a plane extending substantially parallel to a vehicle plane,the vehicle plane defined by a plane through which rotational axes ofwheels of the vehicle pass.
 26. The apparatus according to claim 19, incombination with the vehicle.
 27. The combination according to claim 26,wherein the vehicle is a sport-utility vehicle.
 28. The apparatusaccording to claim 20, further comprising at least one of a compass fordetecting a heading of the vehicle and a thermometer for sensingtemperature, the at least one of the compass and thermometercommunicating with the controller.
 29. The apparatus according to claim28, wherein the controller causes the indicator to switch fromindicating the at least one of the heading of the vehicle and thetemperature to indicating the at least one of pitch angle and roll angleof the vehicle when the rate of change of the at least one of pitchangle and roll angle exceeds a threshold.
 30. A method of detectinginclination of a vehicle, the method comprising: sensing at least one ofpitch angle and roll angle of the vehicle; calculating a rate of changeof the at least one of pitch angle and roll angle; comparing the rate ofchange to a threshold; and warning when the rate of change exceeds thethreshold.
 31. The method according to claim 30, further comprisingindicating the sensed at least one of pitch angle and roll angle of thevehicle.
 32. The method according to claim 30, further comprisingindicating the rate of change of the at least one of pitch angle androll angle of the vehicle.
 33. The method according to claim 30, furthercomprising indicating at least one of a heading of the vehicle and thetemperature.
 34. The method according to claim 30, further comprising:indicating the sensed at least one of pitch angle and roll angle of thevehicle; indicating at least one of a heading of the vehicle and thetemperature; and automatically switching from indicating the at leastone of the heading of the vehicle and the temperature to indicating theat least one of pitch angle and roll angle of the vehicle when the atleast one of pitch angle and roll angle exceeds a threshold.
 35. Themethod according to claim 30, further comprising: indicating the sensedat least one of pitch angle and roll angle of the vehicle; indicating atleast, one of a heading of the vehicle and the temperature; andautomatically switching from indicating the at least one of the headingof the vehicle and the temperature to indicating the at least one ofpitch angle and roll angle of the vehicle when the rate of change of theat least one of pitch angle and roll angle exceeds a threshold.
 36. Amethod of detecting inclination of a vehicle, the method comprising:sensing at least one of a pitch angle and a roll angle of the vehicle;comparing the at least one of sensed pitch angle and roll angle to atleast one threshold; and comparing the at least one of sensed pitchangle and roll angle to a different threshold based upon vehicleoperating conditions; wherein sensing the at least one of pitch angleand roll angle comprises sensing a pitch angle and sensing a roll angle,the method further comprising: comparing the sensed pitch angle to afirst threshold; comparing the sensed roll angle to a second threshold;calculating a combined pitch and roll angle; comparing the combinedpitch and roll angle of the vehicle to a third threshold; and indicatinga warning when the combined pitch and roll angle exceeds the thirdthreshold regardless of whether the sensed pitch angle exceeds the firstthreshold or whether sensed roll angle exceeds the second threshold. 37.The method according to claim 36, wherein comparing the sensed at leastone of pitch angle and roll angle to a different threshold based uponvehicle operating conditions comprises comparing the at least one ofsensed pitch angle and roll angle to a different threshold based uponthe conditions of the surface being traversed by the vehicle.
 38. Themethod according to claim 36, wherein comparing the at least one ofsensed pitch angle and roll angle to a different threshold based uponvehicle operating conditions comprises comparing the at least one ofsensed pitch angle and roll angle to a different threshold based uponthe speed of the vehicle.
 39. A method of reducing false alarms in adevice for detecting inclination of a vehicle, the method comprising:sensing at least one of pitch angle and roll angle of the vehicle;calculating a rate of change of the at least one pitch angle and rollangle of the vehicle; warning only if the rate of change of the at leastone of pitch angle and roll angle of the vehicle exceeds a firstthreshold value and does not exceed a second threshold value.
 40. Themethod according to claim 39, wherein the second threshold is greaterthan the first threshold.
 41. In a vehicle having a vehicle planedefined by the plane through which the rotational axes of the wheels ofthe vehicle pass, a device comprising: a sensor for sensing lateralacceleration of the vehicle in the vehicle plane; a controllercommunicating with the sensor, the controller calculating a rate ofchange of the lateral acceleration and comparing the calculated rate ofchange to a threshold; and an indicator communicating directly orindirectly with the controller, the indicator indicating a warning whenthe calculated rate of change exceeds the threshold.
 42. The deviceaccording to claim 41, in combination with the vehicle.
 43. The deviceaccording to claim 41, wherein the sensor comprises a digitalaccelerometer.
 44. The device according to claim 43, wherein theaccelerometer is a dual axis accelerometer.
 45. The device according toclaim 41, wherein the sensor senses a roll angle of the vehicle andwherein the indicator indicates the roll angle.
 46. The device accordingto claim 43, wherein the accelerometer senses a pitch angle and a rollangle of the vehicle and wherein the indicator indicates the pitch angleand the roll angle.
 47. The device according to claim 41, wherein thethreshold is representative of a driver reaction threshold.
 48. Amultiple use mirror assembly for use in a motor vehicle, the mirrorassembly comprising: a mirror frame having a mirror fixed thereto andmeans for adjustably securing the mirror frame to the motor vehicle; anindicator integrally secured to the mirror assembly and simultaneouslyvisible with reflections in the mirror; and at least one sensor forsensing at least one of pitch angle and roll angle of the motor vehicleindependent of the relative position of the mirror frame and the mirrorrelative to the vehicle and operatively connected to the indicator, theindicator indicating at least one of the sensed pitch angle and rollangle of the vehicle.
 49. The mirror assembly according to claim 48,further comprising a controller communicating with the indicator and theat least one sensor, the controller calculating a rate of change of theat least one of pitch angle and roll angle, wherein the indicatorincludes means for indicating a warning when the rate of change exceedsa first threshold.
 50. The mirror assembly according to claim 49,wherein the indicator includes means for indicating a warning when therate of change is above the first threshold and below a secondthreshold, wherein the first threshold is defined by a recoverable rateof change and the second threshold is defined by a non-recoverable oneof pitch angle and roll angle of the vehicle.
 51. A mirror assembly foruse in a vehicle, the mirror assembly comprising: a frame; a mirrormounted to the frame; and a compass coupled to the frame, the compassdetecting a heading of the vehicle, the compass communicating with acontroller that communicates with a sensor that is responsive to atleast one of pitch angle and roll angle of the vehicle, the controllercorrecting the detected heading of the vehicle based on the sensed atleast one of pitch angle and roll angle of the vehicle; and an indicatormounted to the frame, the indicator indicating the corrected heading.52. The assembly according to claim 51, wherein the indicator indicatesa warning when the at least one of pitch angle and roll angle exceeds athreshold.
 53. The assembly according to claim 51, wherein the indicatorindicates a warning when a rate of change of the at least one of pitchangle and roll angle exceeds a threshold.
 54. The assembly according toclaim 52, wherein the warning is at least one of an audible and a visualwarning.
 55. The assembly according to claim 53, wherein the warning isat least one of an audible and a visual warning.
 56. The assemblyaccording to claim 51, wherein the indicator communicates with athermometer to indicate temperature.
 57. The assembly according to claim51, in combination with the sensor, wherein the mirror assembly furthercomprises a mount to mount the frame to the vehicle, the sensor beingmounted to the mount.
 58. The combination according to claim 57, whereinthe mount, when attached to the vehicle, is stationary relative to thevehicle.
 59. The assembly according to claim 51, in combination with thesensor, wherein the sensor, when the mirror assembly is mounted to thevehicle, is stationary relative to the vehicle.
 60. The assemblyaccording to claim 51, in combination with the sensor and the vehicle,the sensor being mounted within the vehicle and apart from the mirrorassembly.
 61. The assembly according to claim 51, in combination withthe vehicle.
 62. The assembly according to claim 51, in combination withthe sensor, wherein the sensor comprises an accelerometer.
 63. Thecombination according to claim 62, wherein the accelerometer comprises adual-axis accelerometer.
 64. The apparatus according to claim 51,wherein the indicator indicates the at least one of pitch angle and rollangle.